1. Field of Technology
The present application relates to enumeration of a handheld device by a host controller, and more particularly to a method and apparatus to support USB enumeration of such a bus powered handheld device where greater than 100 mA is required to enumerate a main processor associated with the handheld device.
2. Description of the Related Art
As those skilled in the art are aware, a universal serial bus (USB) is a standard port that enables a user to connect USB peripherals (i.e. external devices such as digital cameras, scanners, keyboards, printers, external drives and mice) to a personal computer. The USB Specification Revision 2.0 supports a full-speed signaling bit rate of 12 Mbps (million bits per second). Aside from speed advantages, USB devices can be connected or disconnected without the need to restart the computer, allowing a user to easily attach and detach peripherals. For the above reasons, USB ports have become the industry standard as they are a vast improvement over the serial port standard which preceded them.
In accordance with USB Specification Revision 2.0, the computer to which the USB peripherals are attached includes a host controller which may be a combination of hardware, firmware or software. The host controller is used for: detecting the attachment and removal of USB peripherals; managing control flow between the host controller and the USB peripherals; managing data flow between the host controller and the USB peripherals; and providing power to attached USB devices. As will be appreciated by those in the art, USB devices include “hubs” which provide additional attachment points to the universal serial bus and “functions” such as USB peripherals. The host controller may have integrated therewith a root hub which may connect to other hubs or functions.
In one configuration, a computer (with integral host controller and root hub) connects via a USB port to a handheld communication device (or “function”), such as a cellular phone or a personal digital assistant (PDA), via a vendor-specific adapter. USB handheld charger and sync cables that provide handheld users with a way of charging handheld devices via the USB port on their computer, rather than relying on bulky power adapters and cradles, are known. Data can also be synchronized between the handheld communication device or PDA and the host computer. When a USB peripheral is attached to a powered USB port, the host controller will issue a port enable and reset command to that port. When the port has been enabled, the USB peripheral is now in Default state and can draw no more than 100 mA until it is properly configured. This may be unacceptable for handheld communication devices that may require more than 100 mA to operate.